Trends toward increasing survival of infants born at less than 750 grams (about 1-1/2 pounds) have suggested higher prevalence of complications related to birth and continuing health deficits. Dr. Overpeck documented the status for the births, subsequent deaths, and survival in the U.S. birth cohort of 1983. She has provided background and technological support for staff of the March of Dimes (Joann Petrini) to complete the collaborative analysis to assess changes in survival and mortality of these extremely low birth weight infants. The analysis will compare the baseline years before introduction of surfactant therapy (1983), years incorporating the experimental phase of surfactant therapy (1987-88), and the latest years of available data which include births associated with both surfactant and antenatal corticosteroid therapy (1990-92). Deaths to infants born in the baseline years at weights less than 750 grams (about 24 weeks gestation) contributed about 25 percent of total infant mortality in 1983. Over 40 percent of deaths prior to six days of life were from these smallest least mature infants.